Method of simultaneously transforming a plurality of voice signals input to a communications system

ABSTRACT

A method of simultaneously transforming at least two input voice signals x i  of a communications system ( 30 ), each input voice signal x i  being received at a specific reception frequency F i  and corresponding to the voice of a remote party communicating with a user of the communications system ( 30 ). During an initialization stage, a transformation T i  is allocated to at least one reception frequency F i  of the input voice signals x i , and during a utilization stage, transformations T i  are applied simultaneously to the input voice signals x i  as a function of the reception frequencies F i , modifying at least one characteristic of each of the input voice signals x i . Thus, the voice of each remote party in communication with the user of the communications system ( 30 ) is modified artificially by a transformation T i , thereby making it easier for the user to perceive and discriminate between simultaneous voices from the remote parties.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.13/784,098, filed Mar. 4, 2013, now U.S. Pat. No. 9,087,509; whichclaims priority to France Application No. FR 12 00920, filed Mar. 28,2012; the disclosures of which are incorporated in their entirety byreference herein.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The present invention lies in the field of communications systems. Itrelates to a method of simultaneously transforming voice signals inputto a communications system. The method is intended more particularly forthe communications systems present in aircraft.

(2) Description of Related Art

At present, in the field of aviation in general, and in the field ofrotary wing aircraft more particularly, a pilot uses the communicationssystem of the aircraft to dialog with multiple remote parties, whetheroutside the aircraft or indeed on board the aircraft.

The pilot needs to communicate with air traffic controllers in variouscontrol towers controlling and organizing the traffic of aircraft, andalso with the pilot of other aircraft or indeed with remote parties onthe ground, on board a ship, or on board an oil platform, for example.

The communications system of an aircraft can receive a plurality ofvoice signals, each voice signal being made up of waves that arereceived at a given reception frequency. Each received voice signal isthen transmitted to the pilot by the communications system in the formof the voice of the remote party. The term “input voice signal” is usedto mean a signal received by the communications system and correspondingto the voice of a remote party in communication with the pilot.

For example, high frequency (HF), very high frequency (VHF), or indeedultra-high frequency (UHF) systems are known for performing suchcommunication.

In order to undertake this type of communication, the pilot makes use ofappropriate adjustment means on the communications system to define oneor more reception frequencies. Each reception frequency corresponds tothe frequency of the waves making up each voice signal corresponding tothe voices of the remote parties in communication with the pilot.

Below in the present description, the term “reception frequency of thesignal” is used more simply to designate the frequency of the wavesmaking up the received signal.

The pilot also communicates with people on board the aircraft, such as acopilot, a navigator, or any other person on board the aircraft. Thecommunications system making this possible is sometimes referred to asan “on-board telephone”.

Nowadays, the communications systems present on aircraft enable signalsto be received simultaneously on a plurality of reception frequencies,thus making it possible to communicate simultaneously with a pluralityof remote parties such as a traffic controller, or the pilot of anotheraircraft. In addition, the people on board the aircraft use the samecommunications system, via the on-board telephone to communicate withone another and with the pilot of the aircraft.

A problem then arises when several remote parties, whether external tothe aircraft or on board it, speak simultaneously to the pilot. Sincethe voices of the remote parties are then superposed, theirintelligibility is reduced significantly, and understanding messagesbecomes more complicated.

Furthermore, when the pilot is already in communication with one remoteparty, another message received on another reception frequency can bedifficult to understand or even inaudible. That other message might beimportant, e.g. coming from a traffic controller requesting the pilot ofthe aircraft to change course, and the message might be misunderstood ornot understood at all, and therefore not taken into account by the pilotof the aircraft.

In order to mitigate such problems with present communications systems,the pilot of an aircraft can manually increase the sound volumeassociated with the reception frequency for a signal that corresponds tothe poorly understood message. Conversely, the pilot can lower the soundvolume associated with the reception frequency corresponding to messagesthat are considered as not having priority.

Either way, the pilot temporarily lets go of the flight controls inorder to modify the sound volume associated with the receptionfrequency(ies) of the corresponding signal(s), and that might bedangerous, depending on flying conditions. Furthermore, during the timeit takes to change sound volume, some or all of the messages might bepoorly understood or even not understood at all by the pilot. This canbe dangerous, depending on the importance of the message, particularlyif the pilot needs to perform a maneuver or to take action very quickly.

Finally, the pilot may ask the remote party to repeat the message thathas not been understood or that has been poorly understood. Once again,that can be dangerous if it is necessary for the pilot to maneuver or totake action very quickly.

Under all circumstances, pilot reactivity is degraded by the receivedmessage being poorly understood or not understood at all, and the lossof time this causes can be dangerous if the message is particularlyimportant and rapid reaction is needed.

Nevertheless, if the aircraft has a system for spatializingcommunications, understanding various superposed messages can be madeeasier. For example, according to document U.S. Pat. No. 5,438,623, sucha system makes it possible to transmit the received messages so as togive the impression that they come from different sources placed indifferent locations in the space around the pilot. However, there is nopriority amongst the various messages depending on the remote party,e.g. a traffic controller. There is no transformation of the signal, butmerely a shift in the time the message is perceived, thereby giving theimpression of the source of the corresponding voice being shifted inthree-dimensional space.

Nevertheless, as from about three or four simultaneous messages, thepilot once more perceives voices that are superposed and very difficultto understand, since the spatialization is no longer sufficient forimproving the situation.

There also exists systems for mitigating poor hearing of a user. Suchsystems, e.g. described in documents EP 2 138 009 and US 2002/0111796,serve to modify the characteristics of a voice so as to make it easierto understand by a user having a hearing defect. The characteristics ofthe voice that are modified include sound volume and one or morefrequencies of the voice.

A voice may be resolved into a plurality of tones, each tone beingcharacterized in particular by its frequency. For example, a tone with alow frequency corresponds to a low-pitch tone and a tone with a highfrequency corresponds to a high-pitch tone.

By increasing the frequency of one or more tones making up the voice, itis possible to make it higher pitched, and consequently more distinctivefor certain people.

However, the systems described modify one voice only and they are notcapable of processing a plurality of voices simultaneously.

Elsewhere, the document “Design considerations for improving theeffectiveness of multitalker speech displays”, from the Proceedings ofthe 2002 International Conference on Auditory Display, Kyoto, JP, ofJul. 2, 2002, describes various characteristics that contribute to theintelligibility or lack of intelligibility associated with superposedvoices during multitalker communications, which characteristics may bebackground sounds, the number of talkers, whether or not a talker isknown, the characteristics that are intrinsic to each voice, the soundlevel of each voice, or indeed the spatial position of each voice. Thatdocument also mentions that it is possible to modify one or morecharacteristics of a voice in order to improve its intelligibility, butnevertheless, it does not disclose how those characteristics are to bemodified.

The technological background also contains the documents “A review ofthe cocktail party effect” from Journal of the American Voice I/OSociety, 1992, Vol. 12, pp. 35-50, “Aesthetic and auditory enhancementsfor multi-stream information sonification” from Proceedings of the 3rdInternational Conference on Digital Interactive Media Entertainment andArts, 2008, pp. 224-231, and “Monitoring the simultaneous presentationof spatialized speech signals in a virtual acoustic environment” fromDefense Technical Information Center OAI-PMH Repository, US, Jun. 1,1998, and also document U.S. Pat. No. 5,438,623.

In the description below, the term “frequency of the voice” is used todesignate simply the frequencies of the tones making up the voice. Thesevoice frequencies are completely distinct and independent from thefrequency on which the signal corresponding to the voice is received.

BRIEF SUMMARY OF THE INVENTION

The present invention thus seeks to propose a method that makes itpossible to overcome the above-mentioned limitations.

According to the invention, a method of transforming at least two voicesignals input to a communications system comprises an initializationstage and a utilization stage. Each input voice signal is received at aspecific reception frequency and corresponds to the voice of a remoteparty communicating with a user of the communications system.

During the initialization stage, at least two transformations areapplied to the input voice signals, each transformation being associatedwith at least one reception frequency of the input voice signals andbeing distinct from the other transformations. Thereafter, during theutilization stage, these transformations are applied simultaneously tothe input voice signals as a function of their reception frequencies.Once transformed, the voice signals are directed to an output of thecommunications system, e.g. for delivery to a headset of the user of thesystem.

The method is remarkable in that it makes it possible, during theutilization stage, for a user of the communications system to optimizethe perception of the voices of remote parties, which voices correspondto input voice signals that are received simultaneously.

The transformations make it possible to modify at least onecharacteristic of each input voice signal, and consequently at least onecharacteristic of the voice of each of the remote parties communicatingwith the user of the communications system. Modifiable characteristicsof a voice include in particular its sound volume and the frequencies ofthe voice.

The voice of each remote party communicating with the user of thecommunications system is modified artificially by the or eachtransformation applied thereto, thereby making the voices easier toperceive by the user of the system and consequently enabling them to bediscriminated and understood.

For example, the sound volume of a first voice, corresponding to a firstinput voice signal having a first reception frequency may be increased,while a second voice, corresponding to a second input voice signalhaving a second reception frequency may be modified so as to be higherpitched. A third voice may be modified to be made to sound metallic.

These transformations thus make it possible to avoid the superpositionthat occurs when voices are received simultaneously making themimpossible to understand, in particular by making it easier todiscriminate between them.

A high pitched voice that is simultaneous with a low pitched voice canbe distinguished more easily than two high pitched voices. Similarly, avoice that is made to sound metallic can be distinguished from the othertwo voices. This enables the user of the communications system todistinguish between, and consequently to understand, the voices of thevarious remote parties that correspond to the voice signals received bythe communications system.

Furthermore, each voice of a remote party corresponds to an input voicesignal received at a specific reception frequency. By associating eachtransformation with at least one reception frequency for these inputvoice signals, it is possible to allocate a single transformation toeach input voice signal and consequently to each voice of a remote partycommunicating with the user of the communications system.

Furthermore, by associating a transformation with a reception frequencyfor an input voice signal, and consequently with a voice of a particularremote party, the user is capable of giving priority to certainmessages. By allocating a specific transformation to a signal comingfrom a remote party likely to be delivering an important message, theuser will immediately recognize the transformation on hearing the voiceand can concentrate on that message that might be important. Forexample, the pilot of an aircraft may allocate an increase in soundvolume to a message coming from a traffic controller.

The method may also include one or more additional characteristics.

The voices of the remote parties communicating with the user of thecommunications system are generally received by the communicationssystem in the form of input analog signals. An analog signal is a signalhaving a value that varies continuously. The method of the inventionthen enables transformations to be applied to these input analog signalsin order to modify at least one characteristic of the voice of eachremote party communicating with a user of the communications system.

Nevertheless, it can be advantageous to transform the input analogsignals into digital signals. A digital signal is made up of asuccession of discontinuous values, derived from the analog signal. Thedigital signal is easier to modify than is an analog signal, withvarious transformations being applied to the successive values making itup.

In the method of the invention, the input analog signals are thereforeconverted into digital signals by means of at least oneanalog-to-digital converter. Thereafter, the transformations are appliedto the digital signals in order to obtain transformed digital signals.The transformed digital signals are then converted into transformedanalog signals by means of a digital-to-analog converter. Thesetransformed analog signals correspond to the modified voices of theremote parties, thus enabling the user of the communications system todistinguish between them more easily.

In a preferred implementation of the invention, the analog-to-digitalconverter and the digital-to-analog converter are constituted by asingle converter capable of performing both conversions. For example,the converter may be a codec. The word “codec” is a portmanteau word,i.e. a neologism formed by melding together a portion of each of atleast two existing words, such that “codec” in fact means“coder-decoder”. A codec is thus capable of coding a first signal, e.g.converting an analog signal into a digital signal, and also of decodinga second signal, e.g. converting a digital signal into an analog signal.By way of example, such a codec may be incorporated in a printed circuitor indeed in software that is incorporated in the communications system.

In an implementation of the invention, the initializing stage of thetransformation method, during which a transformation is allocated toeach voice input signal reception frequency, may itself be subdividedinto a plurality of steps.

Firstly, the reception frequencies of the input voice signals that mightbe received by the communications system are input. This inputting isperformed via input means, that may be incorporated in thecommunications system or that may be suitable for being connectedthereto. For this purpose, it is possible to select these receptionfrequencies from a list of reception frequencies stored in storagemeans, or else to input the desired reception frequency values directly.The storage means may be incorporated in the communications system orthey may be suitable for being connected thereto.

Thereafter, the transformations are defined, each transformation beingallocated to at least one of the previously input reception frequenciesand each reception frequency being associated with a singletransformation. During the utilization stage, each transformation isapplied to each input voice signal corresponding to the receptionfrequency(ies) associated with the transformation in question.

In order to define these transformations, each transformation isselected from a list of transformations stored in the storage means ofthe communications system. Thereafter, if necessary, it is possible toadjust the transformation by dedicated adjustment means in order toadapt it to each user of the communications system, thereby improvingthe differences between the voices modified by the transformationrelative to the other transformed voices. Sensitivity to variousdifferent tones can vary from one user to another. It is thereforeadvantageous to be able to adjust each transformation so as to adapt itto the sensitivity of the user.

For example, it is possible to modify the sound volume or one or morefrequencies of the voice corresponding to the input voice signalconcerned by the transformation. The dedicated adjustment means may beincorporated in the communications system or they may be suitable forbeing connected thereto.

Finally, these reception frequencies and the associated transformationsare stored in a dedicated database. This database is stored in thestorage means.

This step thus makes it possible to define all of the receptionfrequencies corresponding to the input voice signals that are to bereceived by the communications system, and also the set oftransformations that are associated with these input voice signals.

In a first implementation of the method, at least one transformation isconstituted by a digital filter. The transformed digital signal asobtained in this way is in compliance with the equation:

${y_{i}(n)} = {{\sum\limits_{k = 0}^{k = {n - 1}}{a_{ik} \cdot {y_{i}( {n - k} )}}} + {\sum\limits_{k = 0}^{k = {n - 1}}{b_{ik} \cdot {x_{i}( {n - k} )}}}}$where x_(i)(n) is the input digital signal and y_(i)(n) is thetransformed digital signal. i and n are integers, with i correspondingto the number of the input voice signal x_(i), and n corresponding tothe rank of a value of the digital signal in the succession ofdiscontinuous values making up the digital signal. The coefficientsa_(ik) and b_(ik) are defined so as to modify at least onecharacteristic of the voice corresponding to the input voice signal andthese coefficients are specific to each transformation T_(i).

For example, at least one transformation is constituted by a digitalfilter of finite impulse response. The transformed digital signal asobtained in this way is in compliance with the equation:y _(i)(n)=x _(i)(n)+α·x _(i)(n−K)The coefficients α and K are defined so as to modify at least onecharacteristic of the voice corresponding to the input voice signal, Kbeing an integer.

In another example, at least one transformation is constituted by adigital filter of infinite impulse response. The transformed digitalsignal as obtained in this way is in compliance with the equation:y _(i)(n)=x _(i)(n)+α·y _(i)(n−K)The coefficients α and K are defined so as to modify at least onecharacteristic of the voice corresponding to the input voice signal, Kbeing an integer.

In a second implementation of the method, at least one transformation isconstituted by a processor module enabling the input voice signal to bemodified in compliance with a known principle generally referred to as“pitch shifting”. The purpose of this transformation is to modify atleast one tone making up the voice of the remote party by at least oneoctave without changing the duration of the tone.

When a tone is shifted by one octave upwards, i.e. so as to obtain atone that is higher pitched, the duration of the tone is normallyshortened, being divided by two. In contrast, pitch shifting makes itpossible to play back a tone that is different by one octave but withoutmodifying its duration. Such a transformation is easier to implement ona digital signal than on an analog signal. The voice corresponding tothe input signal is thus easier to distinguish from other voices.

In a third implementation of the method, at least one transformation isconstituted by a processor module also known as a “vocoder”, which is acontraction of the term “voice coder”. A vocoder is a method ofprocessing a sound signal that enables the main spectral components of avoice to be analyzed and that enables a synthetic voice to be fabricatedon the basis of the result of that analysis and in accordance with thecharacteristics of a carrier signal associated with the processor moduleand defining the transformation.

By way of example, certain vocoders enable the frequencies of a voice tobe offset, such that the voice becomes completely deformed andunrecognizable, while still remaining perfectly comprehensible. Thattechnique is used in particular for making a speaker anonymous.

Each of these transformations enables a signal-to-noise ratio to bepreserved together with properties that guarantee the intelligibility ofvoices that are received simultaneously.

The present invention also provides a communications system. Such acommunications system comprises at least one receiver means suitable forreceiving a plurality of input voice signals, each input voice signalbeing received at a specific reception frequency. Such a system also hasat least one transmitter means for transmitting voice output signals toother parties and at least one processor unit together with at least onestorage means.

The processor unit of the communications system includes calculationmeans that executes instructions stored within the storage means inorder to transform each input voice signal as a function of itsreception frequency so as to enable a user of the communications systemto optimize perception of the voices of the remote parties correspondingto input voice signals that have been received simultaneously.

In an embodiment of the system of the invention, the communicationssystem includes at least one input means for inputting the receptionfrequencies and for selecting the transformations from a list oftransformations stored in the storage means. Thereafter, thecommunications system makes it possible to allocate each transformationto at least one of the reception frequencies that have been input.Finally, these reception frequencies and the associated transformationsare stored in the storage means.

In an embodiment of the invention, the communications system includes atleast one adjustment means for adjusting the transformations. Thetransformed voice can thus be adapted to each user of the communicationssystem, thereby improving the differences between the voices modified bythe transformation relative to the other transformed voices.

In an other embodiment of the invention, the communications systemincludes at least one analog-to-digital converter for converting theinput voice signals into digital signals prior to applying theassociated transformations thereto. The communications system alsoincludes at least one digital-to-analog converter for converting thedigital signals as transformed by the transformation into transformedanalog voice signals. The analog-to-digital converter and thedigital-to-analog converter may be constituted by the same converter,e.g. a codec, so as to simplify the system.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The invention and its advantages appear in greater detail from thecontext of the following description of embodiments given by way ofillustration and with reference to the accompanying figures, in which:

FIG. 1 is a block diagram of the method of the invention;

FIG. 2 shows a communications system of the invention; and

FIG. 3 shows a principle for transforming input voice signals.

Elements that are present in more than one of the figures are given thesame references in each of them.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a block diagram of the transformation method of the invention,comprising two steps: an initialization stage 10 and a utilization stage20.

FIG. 2 shows a communications system comprising receiver means 31,transmitter means 32, and a processor unit 33.

The receiver means 31 are suitable for receiving a plurality of inputvoice signals x_(i), each input signal x_(i) being received at aspecific reception frequency F_(i) and corresponding to the voice of aparty in communication with a user of the communications system 30.

The communications system 30 also has storage means 35, input means 36,and adjustment means 39.

In the method of the invention, during the initialization stage 10, atleast two transformations T_(i) are applied to the input voice signals,each transformation T_(i) being associated with at least one receptionfrequency F_(i) and being distinct from the other transformations.

Then, during the utilization stage 20, these transformations T_(i) areapplied simultaneously to the input voice signals x_(i) of correspondingreception frequencies F_(i), thereby transforming each input voicesignal x_(i) so as to optimize reception of the voice of that party bythe user.

For this purpose, the processor unit 33 of the communications system 30has calculation means executing instructions stored within the storagemeans 35 for transforming each input voice signal x_(i). Thereafter,each transformed voice signal y_(i) is directed to an output 34 of thecommunications system 30, e.g. in order to be delivered to a headset ofa user of the communications system 30.

The voice of the other party is thus artificially modified, by modifyingat least one of the characteristics of that voice, such as its soundvolume or its frequency.

During this initialization stage 10, said reception frequencies F_(i) ofthe input voice signals x_(i) are input via the input means 36, and thenthe transformation T_(i) to be applied to each reception frequency F_(i)is selected from a list of transformations stored in the storage means35. i is an integer and corresponds to a number of the input voicesignal x_(i).

Thereafter, these reception frequencies F_(i) and the associatedtransformations T_(i) are stored in a dedicated database within thestorage means 35.

It is also possible to adjust the transformation T_(i) using theadjustment means 39. This makes it possible in particular to adapt thetransformation T_(i) to each user so as to optimize the distinctionsbetween voices that are received and transformed simultaneously.

During the utilization stage 20, it is possible to apply to each inputvoice signal x_(i) the transformation T_(i) associated with thereception frequency F_(i) of the input voice signal x_(i), therebyobtaining a transformed voice signal y_(i).

During the utilization stage 20, it is then preferable for eachtransformation to be applied to a digital signal x_(i)(n). FIG. 3 showsanalog-to-digital converters 37 and digital-to-analog converters 38present in the communications system 30. For this purpose, theanalog-to-digital converter 37 is used to convert the input voicesignals x_(i) into digital signals x_(i)(n), where n is an integercorresponding to the rank of a value in the digital signal sequenceselected from the succession of discontinuous values making up thedigital signal.

Thereafter, the transformation T_(i) associated with the receptionfrequency F_(i) of the input voice signal x_(i) is applied to eachdigital signal x_(i)(n) by means of a processor unit 33, therebyobtaining the transformed digital signal y_(i)(n).

Finally, these transformed digital signals y_(i)(n) are converted intotransformed analog voice signals y_(i) by a digital-to-analog converter38 present in the communications system 30.

In a preferred embodiment of the invention, the analog-to-digitalconverter 37 is constituted by a codec, and the digital-to-analogconverter 38 is also constituted by the same codec.

A digital signal is made up of a succession of discontinuous values,while an analog signal is made up of a value that varies continuously.It is easier to apply transformations to discontinuous values, i.e. to adigital signal, than to a continuous value, i.e. to an analog signal.

Nevertheless, in a variant of the invention, each transformation may beapplied to analog signals, however, the performance is diminished.

The transformations T_(i) applicable to the digital signal x_(i)(n) maybe constituted by a digital filter enabling a transformed digital signaly_(i)(n) to be obtained in application of the equation:

${y_{i}(n)} = {{\sum\limits_{k = 0}^{k = {n - 1}}{a_{ik} \cdot {y_{i}( {n - k} )}}} + {\sum\limits_{k = 0}^{k = {n - 1}}{b_{ik} \cdot {x_{i}( {n - k} )}}}}$where i is an integer corresponding to the number of the input voicesignal x_(i), and n is an integer corresponding to the rank of the valueof the digital signal in the succession of discontinuous values makingup the digital signal, and where the coefficients a_(ik) and b_(ik) arespecific to each transformation T_(i) and are defined in order to modifyat least one of said characteristics of said voice of said other party.

For example, a transformation T_(i) may be a digital filter of finiteimpulse response serving to obtain a transformed digital signal y_(i)(n)in application of the equation:y _(i)(n)=x _(i)(n)+α·x _(i)(n−K)where α and K are defined so as to modify at least one of saidcharacteristics of said voice of said other party, K being an integer.

Likewise, a transformation T_(i) may be constituted by a digital filterof infinite impulse response enabling a transformed digital signaly_(i)(n) to be obtained in application of the equation:y _(i)(n)=x _(i)(n)+α·y _(i)(n−K)where α and K are defined in order to modify at least one of saidcharacteristics of said voice of said other party, K being an integer.

In an embodiment of the invention, a transformation T_(i) may beconstituted by a processor module serving to modify at least one tone ofsaid voice by at least one octave without modifying the duration of thattone.

In another embodiment of the invention, a transformation T_(i) may beconstituted by a processor module serving to analyze at least onespectral component of said voice and to fabricate a synthetic voice fromthe result of that analysis and in application of characteristics of acarrier signal associated with that processor module.

Each of the transformations serve to preserve a signal-to-noise ratioand properties that guarantee the intelligibility of voices receivedsimultaneously.

Naturally, the present invention may be subjected to numerous variationsas to its implementation. Although several embodiments are described, itwill readily be understood that it is not conceivable to identifyexhaustively all possible embodiments. It is naturally possible toenvisage replacing any of the means described by equivalent meanswithout going beyond the ambit of the present invention.

What is claimed is:
 1. A method of communicating at least two voicesignals x_(i) input simultaneously to a communications system to a userof the communications system, each input voice signal x_(i) beingreceived by a receiver of the communications system at a specificreception frequency F_(i) and corresponding to a voice of a remote partyin communication with a user of the communications system, the receptionfrequency of each input voice signal x_(i) being distinct andindependent of voice frequencies of the voice of the remote partycorresponding to the input voice signal, i being an integercorresponding to a number of the input voice signal x_(i), the methodcomprising: during an initialization stage, allocating, via a processorof the communications system, transformations T_(i) to the receptionfrequencies F_(i) of the input voice signals such that eachtransformation T_(i) is associated with a respective one of thereception frequencies F_(i) of the input voice signals x_(i), eachtransformation T_(i) being distinct from the other transformations inmodifying voice characteristics; and during a utilization stage,applying, by the processor of the communications system, thetransformations T_(i) to the input voice signals x_(i) as a function ofthe reception frequencies F_(i) of the input voice signals x_(i) therebytransforming each input voice signal x_(i) with the transformation T_(i)associated with the reception frequency F_(i) of the input voice signalx_(i) into a transformed voice signal y_(i) in which the voicefrequencies of the voice of the remote party corresponding to the inputvoice signal x_(i) are modified in order to optimize the perception andthe discrimination of the voices of the remote parties by the user andthereby allow the user to concentrate on the voice of the remote partylikely to deliver an important message, and outputting, by an output ofthe communications system, the transformed voice signals y_(i) for theuser of the communications system to hear.
 2. The method according toclaim 1, wherein, during the initialization stage: each receptionfrequency F_(i) for the input voice signals x_(i) is input to theprocessor of the communications system; each transformation T_(i)allocated to at least one reception frequency F_(i) is defined; and thereception frequencies F_(i) and the associated transformations T_(i) arestored in a dedicated database.
 3. The method according to claim 2,wherein during the initialization stage, in order to define eachtransformation T_(i): the transformation T_(i) is selected from a listof transformations.
 4. The method according to claim 1, wherein, theinput voice signals x_(i) are analog input voice signals x_(i) andduring the utilization stage: the analog input voice signals x_(i) areconverted into digital signals x_(i)(n), each made up of a succession ofdiscontinuous values, by an analog-to-digital converter, where n is aninteger corresponding to the rank of a value of the digital signalx_(i)(n) in the succession of discontinuous values; the transformationT_(i) associated with the reception frequency F_(i) of the input voicesignal x_(i) is applied to each digital signal x_(i)(n) by theprocessor, thereby obtaining a transformed digital signal y_(i)(n); andthe transformed digital signals y_(i)(n) are converted into thetransformed voice signals y_(i) by a digital-to-analog converter wherebythe transformed voice signals y_(i) are analog transformed voicesignals.
 5. The method according to claim 4, wherein theanalog-to-digital converter is constituted by a codec, and thedigital-to-analog converter is also constituted by the codec.
 6. Themethod according to claim 4, wherein at least one transformation T_(i)is constituted by a digital filter enabling a transformed digital signaly_(i)(n) to be obtained in application of the equation:${y_{i}(n)} = {{\sum\limits_{k = 0}^{k = {n - 1}}{a_{ik} \cdot {y_{i}( {n - k} )}}} + {\sum\limits_{k = 0}^{k = {n - 1}}{b_{ik} \cdot {x_{i}( {n - k} )}}}}$where i is an integer corresponding to a number of the input voicesignal x_(i), and n is an integer corresponding to the rank of a valueof the digital signal x_(i)(n) in the succession of discontinuousvalues, a_(ik) and b_(ik) being specific to each transformation T_(i)and being defined so as to modify at least one of the characteristics ofthe voice of the remote party.
 7. The method according to claim 4,wherein at least one transformation T_(i) is constituted by a digitalfilter of finite impulse response enabling a transformed digital signaly_(i)(n) to be obtained in application of the equation:y _(i)(n)=x _(i)(n)+α·x _(i)(n−K) where α and K are defined so as tomodify at least one of the characteristics of the voice of the remoteparty, K being an integer.
 8. The method according to claim 4, whereinat least one transformation T_(i) is constituted by a digital filter ofinfinite impulse response enabling a transformed digital signal y_(i)(n)to be obtained in application of the equation:y _(i)(n)=x _(i)(n)+α·y _(i)(n−K) where α and K are defined so as tomodify at least one of said characteristics of the voice of the remoteparty, K being an integer.
 9. The method according to claim 4, whereinat least one transformation T_(i) is constituted by the processorserving to analyze at least one spectral component of the voice and tofabricate a synthetic voice on the basis of the result of that analysisand depending on the characteristics of a carrier signal associated withthe processor.
 10. The method according to claim 1, wherein at least onetransformation T_(i) is constituted by the processor enabling at leastone tone of the voice to be modified by at least one octave withoutmodifying the duration of the tone.
 11. A communications system,comprising: at least one receiver configured to receive a plurality ofinput voice signals x_(i) simultaneously, each input voice signal x_(i)being received at a specific reception frequency F_(i) and correspondingto a voice of a remote party in communication with a user of thecommunications system, the reception frequency F_(i) of each input voicesignal x_(i) being distinct and independent of voice frequencies of thevoice of the remote party corresponding to the input voice signal, ibeing an integer corresponding to a number of the input voice signalx_(i); a processor; a memory configured to store transformations T_(i)associated with the reception frequencies F_(i) of the input voicesignals, each transformation T_(i) being associated with a respectiveone of the reception frequencies F_(i) and being distinct from the othertransformations in modifying voice characteristics; the processorconfigured to transform each input voice signal x_(i) with thetransformation T_(i) associated with the reception frequency F_(i) ofthe input voice signal x_(i) into a transformed voice signal y_(i) inwhich the voice frequencies of the voice of the remote partycorresponding to the input voice signal x_(i) are modified in order tooptimize the perception of the discrimination between the voices of theremote parties by the user and thereby allow the user to concentrate onthe voice of the remote party likely to deliver an important message;and an output configured to output the transformed voice signals y_(i)for the user of the communications system to hear.
 12. Thecommunications system according to claim 11, further comprising an inputconfigured to receive a list of the reception frequencies F_(i), enablethe user to select the transformations T_(i) from a list oftransformations stored in the memory, and enable the user to associateat least one transformation T_(i) to at least one reception frequencyF_(i), the frequencies F_(i) and the associated transformations T_(i)being stored in the memory.
 13. The system according to claim 11,further comprising an input configured to enable a user to adjust thetransformations T_(i).
 14. The system according to claim 11, furthercomprising at least one analog-to-digital converter for converting theinput voice signals x_(i) into digital signals x_(i)(n) made up of asuccession of discontinuous values prior to the transformation T_(i)being applied thereto, thereby transforming them into a transformeddigital signal y_(i)(n), and at least one digital-to-analog converterfor converting the digital signals y_(i)(n) as transformed by thetransformation T_(i) into transformed analog voice signals y_(i), nbeing an integer corresponding to the rank of a value of the digitalsignal x_(i)(n) in the succession of discontinuous values.